Respiration and mineralisation of N were measured in a set of contrasting soils that had either been autoclaved, air-dried, fumigated (with chloroform or methyl bromide) or exposed to gamma radiation. The soils used were a manured and an unmanured arable soil, an acid and a neutral woodland soil, an arable sandy soil and an organic soil under grass. With the exception of the acid woodland soil, the flushes of decomposition (i.e. the increases in O2 consumption, CO2 evolution and N mineralisation that occurred when the treated soil was inoculated and incubated for 10 days) were in the order: air-drying < CH3Br ⩽ CHCl3 < irradiation < autoclaving. All of the treatments, except air-drying, decreased the ratio (C mineralised after treatmcnt)/(N mineralised after treatment). All of the treatments increased the amount of 1N K2SO4 extractable organic C, autoclaving causing by far the greatest increase.

Neither of the fumigants increased respiration in the acid soil over the whole 10 day period, although N mineralisation was slightly increased. Irradiation, air-drying and autoclaving did, however, produce a flush in the acid soil, the order being: irradiation < air-drying < autoclaving. A soluble substrate, extracted from yeast cells by ultrasonic disintegration, decomposed to about the same extent in neutral and in acid soil. When 14C labelled glucose was added to the acid soil and incubated for 52 days, the retention of labelled C was slightly greater (31·6%) than in a comparable near-neutral soil (28·8%). However, the flush that followed fumigation of the acid soil was only half that in the near-neutral soil, suggesting that less biomass is formed under acid conditions. Liming increased the size of the flush in an acid soil.

For soils from the same field but under different management, the size of the flush caused by CHCl3 is in the order: grassland > cropped arable > bare fallow. The flush is much more sensitive to differences in soil management than is the total amount of soil organic matter; a fallowed soil lost half its organic C in 10 yr whereas the increase in respiration that followed fumigation fell to one-seventh its original value. Two Nigerian soils behaved similarly; a soil that had been 2 years under cultivation contained only 16% less total organic C than an adjacent soil still under secondary forest, yet the flush in the cultivated soil was half that in the forest soil. The amount of substrate metabolised during the flush is thus very sensitive to changes in soil management that alter the amount of fresh organic matter entering the soil each year.

Powlson, D. S. 1999. Some causes of error and confusion in field experiments with 15N. Report of the 3rd Research Coordination Meeting of the FAO/IAEA Coordinated Research Project on the Use of Isotope Techniques in Studies on the Management of Organic Matter and Nutrient Turnover for Increased Sustainable Agricultural Production and Environmental Preservation (D1-40.08), Rabat, 6-10 September 1999 . pp. 6-8

Wu, J., Brookes, P. C. and Jenkinson, D. S. 1996. Evidence for the use of a control in the fumigation-incubation method for measuring microbial biomass carbon in soil. Soil Biology and Biochemistry. 28, pp. 511-518.

Jenkinson, D. S., Bradbury, N. J. and Coleman, K. 1993. How the Rothamsted Classical Experiments have been used to develop and test models for the turnover of carbon and nitrogen in soil. Insight from Foresight. Abstracts Rothamsted 150th Anniversary Conference, Harpenden, July 1993 .

Patra, D. D., Brookes, P. C., Coleman, K. and Jenkinson, D. S. 1990. Seasonal changes of soil microbial biomass in an arable and a grassland soil which have been under uniform management for many years. Soil Biology and Biochemistry. 22, pp. 739-742.

Brookes, P. C., Jorgensen, R. G. and Jenkinson, D. S. 1990. The ATP content and adenylate charge of the soil microbial biomass and the effects of temperature on microbial survival and the mineralization of soil organic matter. &nbsp;Transactions of the 14th Congress of the International Society of Soil Science , pp III.239. ISSS, Kyoto..

Jenkinson, D. S. 1977. Studies on the decomposition of plant material in soil .V. The effects of plant cover and soil type on the loss of carbon from C-14 labelled ryegrass decomposing under field conditions. Journal of Soil Science. 28 (3), pp. 424-434.

Jenkinson, D. S. 1965. The decomposition of labelled plant material in soil. Proceedings of the Eleventh Easter School in Agricultural Science, University of Nottingham, 1964. University of Nottingham 1964 Butterworths.

Jenkinson, D. 1963. The priming action. Report of the FAO/IAEA Technical Meeting Organized by the Food and Agriculture Organization of the United Nations and the International Atomic Energy Agency in cooperation with the International Soil Society Brunswick-Volkenrode, 9-14 September, 1963. Volkenrode 09 Sep 1963 Pergamon Press.

Jenkinson, D. 1963. Experimental techniques for using Carbon-14 in studies of soil organic matter. Report of the FAO/IAEA Technical Meeting Organized by the Food and Agriculture Organization of the United Nations and the International Atomic Energy Agency in cooperation with the International Soil Society Brunswick-Volkenrode, 9-14 September, 1963. Volkenrode 09 Sep 1963 Pergamon Press.

Jenkinson, D. 1963. The turnover of organic matter in soil. Report of the FAO/IAEA Technical Meeting Organized by the Food and Agriculture Organization of the United Nations and the International Atomic Energy Agency in cooperation with the International Soil Society Brunswick-Volkenrode, 9-14 September, 1963. Volkenrode 09 Sep 1963 Pergamon Press.